INFLUENCE OF OXIDATIVE STRESS ON MEMBRANE-POTENTIAL AND ON K+ CHANNELS IN NEURONAL CELLS

In the present study, we analyse the effect of oxidative stress induce d by ascorbate(1.5 mM)-Fe2+(7.5 mu M) on the membrane potential of ret inal cells in culture, as determined by the uptake of [H-3]TPP+ (tetra phenylphosphonium), at low and high extracellular K+ concentration [K](0). At resting conditions ([K+](0) = 4 mM), the [H-3]TPP+ accumulate d by control (195.6 +/- 8.0 dpm (mu g protein)(-1)) and peroxidized ce lls (190.0 +/- 7.5 dpm (mu g protein)(-1)) was not significantly diffe rent. At higher extracellular K+ concentrations, the amount of [H-3]TP P+ taken up by peroxidized cells was significantly lower than that tak en up by control cells. The antagonists of glutamate receptors, MK-801 (1 mu M) and CNQX(2 mu M), were without effect on [H-3]TPP+ accumulat ion at [K+](0) = 50 mM. At resting conditions 4-aminopyridine (4-AP; 1 00 mu M) and alpha-dendrotoxin (alpha-DTX, 100 nM), which block the I- D and I-A currents respectively, decreased the uptake of [H-3]TPP+, an d this effect is higher in peroxidized cells. gamma-Dentrotoxin, a blo cker of I-M current, reduced significantly the [H-3]TPP+ uptake only i n peroxidized cells. Under depolarizing conditions ([K+](0) = 15 mM), 100 mu M and 1 mM 4-AP reduced the [H-3]TPP+ accumulation by a similar extent in control cells, but were without effect under oxidative stre ss. Moreover, 100 nM alpha-DTX, which is expected to block the I-K cur rents activated under depolarizing conditions, decreased by about 40% the [H-3]TPP+ uptake in both control and peroxidized cells. Charybdoto xin (10 nM) and apamin (10 nM), which block off I-C and I-AHP currents respectively, were without effect on the [H-3]TPP+ uptake, under rest ing conditions and during clamped depolarization. The results show tha t the cells submitted to oxidative stress are more sensitive to K+ dep olarization and it is suggested that those cells have a higher firing rate frequency. The channels responsible for I-D currents are the most affected by peroxidation.